January 29, 2014
Monkeys And Humans Share Many Brain Similarities, But Not All
April Flowers for redOrbit.com - Your Universe Online
A new study from Oxford University researchers suggests a surprising degree of similarity in the organization of brain regions that control language and complex thought processes in humans and monkeys, as well as key differences. The team's finding demonstrate valuable insights into the evolutionary processes that established the link between humans and other primates and what made humans distinctly different.
The research team performed MRI scans of 25 adult volunteers — 14 women and 11 men — to identify key components in the ventrolateral frontal cortex area of the human brain. Scientists have known for more than 150 years that the ventrolateral region is important to cognitive processes such as language, cognitive flexibility and decision making.
"It has been argued that to develop these abilities, humans had to evolve a completely new neural apparatus; however others have suggested precursors to these specialized brain systems might have existed in other primates," explained Dr. Franz-Xaver Neubert, also of the University of Oxford.
Some parts of the ventrolateral region are implicated in conditions like ADHD, drug addiction and compulsive behavior disorders. The damage of a stroke or neurological disease in other parts of the region can cause difficulties with language. Having a better understanding of how the neural connections of this area work, and the networks involved, should further our understanding of changes in the brain that go along with these conditions.
The team also performed MRI scans on 25 macaque monkeys to compare the ventrolateral frontal cortex connectivity and architecture in both species. Similarities in the connectivity of these regions surprised the scientists. These similarities suggest that some uniquely human cognitive traits may rely on an evolutionarily-conserved neural apparatus that initially supported different functions.
According to Professor Rushworth, "The brain is a mosaic of interlinked areas. We wanted to look at this very important region of the frontal part of the brain and see how many tiles there are and where they are placed. We also looked at the connections of each tile – how they are wired up to the rest of the brain – as it is these connections that determine the information that can reach that component part and the influence that part can have on other brain regions."
The scans allowed the research team to divide the human ventrolateral frontal cortex into 12 areas found to be consistent across all test subjects.
"Each of these 12 areas has its own pattern of connections with the rest of the brain, a sort of 'neural fingerprint', telling us it is doing something unique," said Professor Rushworth.
The 12 regions were compared with the organization of the macaque brains. The team found that 11 of the 12 areas were present in both species, and were connected with other brain regions in very similar ways.
The final region of the ventrolateral frontal cortex of the humans, however, had no equivalent in the macaque. This region is known as the lateral frontal pole prefrontal cortex.
"We have established an area in human frontal cortex which does not seem to have an equivalent in the monkey at all," says Neubert. "This area has been identified with strategic planning and decision making as well as 'multi-tasking'."
Other key differences between the human and monkey brains were also found, most notably in the way the ventrolateral frontal cortex circuits in the two species differ in the way that they interact with brain areas involved with hearing.
"This could explain why monkeys perform very poorly in some auditory tasks and might suggest that we humans use auditory information in a different way when making decisions and selecting actions," says Dr. Neubert.
The scientists found it interesting that the areas the two species have in common are those thought to play a role in psychiatric disorders such as ADHD, OCD and drug abuse. The findings might lead to advances in therapeutic insights.
The results were published in a recent issue of Neuron.
Image 2 (below): Caption: (A) The right vlFC ROI. Dorsally it included the inferior frontal sulcus and, more posteriorly, it included PMv; anteriorly it was bound by the paracingulate sulcus and ventrally by the lateral orbital sulcus and the border between the dorsal insula and the opercular cortex. (B) A schematic depiction of the result of the 12 cluster parcellation solution using an iterative parcellation approach. We subdivided PMv into ventral and dorsal regions (6v and 6r, purple and black). We delineated the IFJ area (blue) and areas 44d (gray) and 44v (red) in lateral pars opercularis. More anteriorly, we delineated areas 45 (orange) in the pars triangularis and adjacent operculum and IFS (green) in the inferior frontal sulcus and dorsal pars triangularis. We found area 12/47 in the pars orbitalis (light blue) and area Op (bright yellow) in the deep frontal operculum. We also identified area 46 (yellow), and lateral and medial frontal pole regions (FPl and FPm, ruby colored and pink). Credit: Neuron, Neubert et al.